Telephonograph



Sept. 7, 1937;

P. H. Rows 2,092,024

TELEPHONOGRAPH Filed March 20, 1953 I 2 Sheets-Sheet 1 mino sses." Imurnlor:

Sept. 7, 193 7.

' P. H. RWE I 2,092,024 J TELEPHONOGRARH Filed Marh 20, 1933 2 Sheets-Sheet 2 l fiinessesz Inventor:

Patented Sept. 7, 1937 ari-:1 sires aosaeac assesses Pauli Henry Rowe, lilos iingeies, @aiif. Application mean recs. desist no. iitifldi.

s 1 lei. ne -aces) This invention relates to sound recordation and reproduction with magnetic records.

A. broad'object or the invention is to improve 7 the quality of sound reproduction from magnetic .1 records,

Another object is to provide a simple and practicable structure for supporting and driving an endless telegraphone wire oi substantial length in Fig. 1 is a diagram illustrating the respective dimensions of the recording and reproducing pole pieces in a telegraphone in accordance with my invention; p

Fig. 2 is a diagram illustrating a recording pole structure having an air gap therein for use in my 7 telegraphone;

Fig. 3 is a diagram showing the shape of erasing pole pieces in accordance with my invention; Fig. 4 is a plan view of an apparatus for supporting an endless telephone record wire in ac cordance with my invention;

Fig-5 is an elevation view with portions broken away of the apparatus shown in plan in Fig. 4.

The telegraphone or magnetic phonograph was recommended for this purpose by Valdemar .Poulsen in his original patent, (U. S. Patent 661,619) andlias the great advantage of being the only method of recording which permits, the use of the same record medium for an unlimited 35 number of records. However, despite this advantage, telegraphones have never come into ex-' tensive use, although the principal was patentedas early as 1900. The main reason for this has been the fact that in the process of telegraphonic recording and reproduction, sounds were badly distorted. The present inventor has, through extensive research, determined that this distortion is caused by five factors: (a) The magnetic flux preading along the recording medium. (b)

' Non-linearity of the magnetization curve of the recording magnet cores. (0). Variations in the permeability of the recording magnet cores with varying flux densities. (11) Non-uniformity of the ratio of residual magnetism recorded on the recording medipm to the flux density of the recording magnet. (e) Residual magnetismin the magnet cores and extraneous residual magnetism on the recording medium.

55 The spreading of the flux along the recording medium is byfar thelargest single factor in immediate vicinity of the recording medium..

soldered, or otherwise fastened, to the pole pieces causing distortion. The cause of this spree. is va. phenomenon known as magnetic fringing, v which takes place whenever a magnetic flux passes from a body of high permeability into one of lower permeability. The hard steel used in 5 '.most telegraphones as a recording medium has generally a much lower magnetic permeability thanthe soft iron pole pieces, therefore, bringing takes place whenever the flux passes. This causes a severe distortion of the higher ire uen- 1 cies when the record is reproduced in the usual manner. The inventor has discovered that this particular form of distortion can be eliminated by using reproducing pole pieces which are so designed as to covers. greater portion of the length 15 tr the wire than the recording pole-pieces cover. The reason for this can be explained as follows: Referring to Fig. l the recording pole pieces (a) have an actual width at; however, due to magnetic fringing the efiective width is greater than the actual width. This efiective width is marked de- 1! the flux in the reproducing magnet cores is to vary in exactly the same manner as the flux in the recording magnet cores varied, a condition which is necessary for distortionless reproduction, the width of the reproducing pole'pieces (e) must be equal to the efiective width 'of the recording pole pieces; hence, by using a wider pole piece for reproducing, distortion due to fringing is elimie nated. The actual widths of the pole pieces are immaterial as-faras this invention is concerned, the relative width being the only important iac- 4 tor. The size of the magnet core which may or may not be one and the same piece with the pole 4 pieces, is not important. In the event that the v magnet core and the pole piece'is one and the same body, the designation pole pieceshall refer to that portion of the magnet core in the In order that the effective width of the record ing pole pie ces and the actual width of the reproducing pole pieces may be kept small enough to I afiord good reproduction of the higher frequencies consistent with low wire speeds, the actual width of the recording pole pieces must be made very small. This has the disadvantage of making them exceedingly. weak mechanically so that they are rapidly-worn-"away bythe moving wire. To rectify this trouble a non-magnetic material is so asto afford a reinforcement mechanically and l to reduce the wear of the pole pieces by increasing thearea of contact with the wire. This reinforcement is shown in Fig.2 'at (b) Distortion due to non-linearity of the magnetiluctance of the magnetic circuit to the point where the characteristics of the circuit are pracmagnet is eliminated by reason of the great mag subsequently will generally be a small amount of residual netism left in this wire,

tically the characteristics of the air gap. :It is well known that the permeability of air is practically constant and the magnetization curve of air is practicallya straight line. Therefore, byf

using a magnetic circuit with .a large air gap, distortion, due to non-linearity of the magnetization,

curve and variations in the permeability of the recording magnet cores, is eliminated. This air gap is shown in Fig. 2 at (g). x Q

Distortion due to variations in the ratio of re sidual magnetism recorded on the recording medium to the flux density in the recording pole pieces, is eliminated by using such a narrow rangeof flux densities for recording that these variations become negligible. This, of course, results in a very weak record. However, the intensity of the record is of no importance because the faintest record can be amplified to level by means of vacuum tubes.

By using an air gap, as shown in Fig. 2, in the circuit of the recording magnet, the eifect of residual magnetism in the core of this recording netic reluctance of said air gap. By using recording pole pieces of very small physical dimensions the residual magnetism of the pole pieces becomes null for all practical purposes.

In order that telegraphonic records shall be free from disturbing noises, which may also cause distortion, the recording medium must be' free from any residual magnetic flux before the record is impressed upon it. If a telegraphone wire has had a previous record recorded on it and this previous record has been erased by means of a constant magnetic field, as is customary, there L magcaus'ing distortion and noise. To remedy this, the inventor uses an alterhating-current erasing device, shown in Fig. 3. sir; alternating current is sent through the coils c the magnet core and the pole pieces, (,0 These pole pieces are tapered at either side, thus causing the magnetic flux to spread out over a wide area along the recording medium (m) and to gradually decrease to either side of the pole pieces, as shown by the line (i) This line represents the flux density. The frequency of the al-v when it has passed out of the erasing field en tirely.

By using all of the above mentioned improvements-a telegraphonic record may be made and reproduced with practically perfect tone fidelity. By reason ofthis improved tone quality, the telegraphone, aside from making possible a very simple and practical telephongraph will also find application in many other fields wherein it has previously useless because of distortion.

By using an endless wire as a recording m diany desired volume I This causes an alternating flux to flow in um, the telegraphone will continually repeat the messageor other collection of sounds recorded.

small space. The inventor hasdevised a means I for doing-this in a very simple manner. a

Referring to Fig. '4, grooved rollers (8) are placed at intervals around the circumference of a circle. These rollers are free to rotate about their individual shafts (ll), only, otherwise they are held rigidly in position bythe end plates (9).

These end plates being supported by the central members (I0) and rigidly attached thereby to the base (l3). The grooves in the individual rollers are circular. However, the shoulder pieces (I 4) which determine the positions of the rollers axially are of different sizes as can be seen in Fig. 5. This is to cause the grooves of adjacent rollers in each group to lie on a cylindrical spiral. The recording wire (I2) is wound about one of these groups of rollers as shown in Fig. 5. Assuming that the wire enters at the bottom of the group of rollersit then travels in a spiral about all six rollers emerging at the top of the opposite side. Then the wire passes to the next group of rollers and travels on a similar spiral in a downward direction and emerges opposite the point of origin where the wire is connected, thus forming an endless wire which may be moved over an endless path. Motion can be imparted to the wire by rotating one or more of the individual rollers by any conventional means.

Having described my invention, 1 claim:

' 1. A telegraphdne comprising a record medium of high magnetic retentivity, a recording pole 'netization' of said reproducing pole piece for reproducingv signal impulses in accordance with said varying magnetization, and means for moving said variably magnetized record medium past said reproducing pole piece to variably magnetize,

the latter in accordance with said signal impulses; in which said recording pole piece is of smaller dimension in the, direction of movement of said .medium than said reproducing pole'plece.

2. A telegraphone as described in claim 1 in which said recording pole piece consists of material of low magnetic retentivity.

3. A telegraphone comprising a record medium of high retentivity, a recording pole piece positioned adjacent said medium and adapted to be variably magnetized in response to signal impulses, and means for moving said record medium relative to said recording pole piece whereby said record medium is variably magnetized longitudinally in accordance with signal impulses; in which said recording pole piece is fixed with respect to the path of movement-oi said medium and comprises a tip section for magnetizing said record medium and a coil section in the field 01' a magnetic coil, with an air gap be n said two sections.

. 4. A telegraphone comprising a record medium of high retentivity, I tioned adjacent said medium. and adapted to be variably magnetized in response to signal impulses, means for moving said record medium, means ior preparing said medium to receive a '70 a recording pole piece p081- 1 value at a point spaced therefrom on the trailing 7 magnetic recording comprising a pole piece, shaped and positioned to closely approach said medium at one point 3 and gradually recede from said medium on the trailing side of said one point,

whereby the magnetic coupling between the medium and pole piece gradually diminishes from maximum value at one point to substantially zero side. and means for producing an altema'ting magnetic flux in said pole piece.

5. Apparatus for movably supporting an endless telegraphone wire oi substantial length in compact space comprisinga plurality of juxtaposed rollers positionedwith their axes paralleljstationarymeans for supporting each roller for'rotation about its axis, each roller having a Diurality of grooves spaced longitudinally therealong, 'each groove extending concentrically about its roller and the grooves of successive rollers being.

displaced-.longitudinallyin one direction whereby corresponding grooves in successive rollers define a helical pathextending around the entire group of rollers and of pitch equal to the'tlistancebetween successive grooves on each roller," and 

